LED luminaires have previously been constructed with a focus on a high luminance and a high heat dissipation density, to be precise primarily driven by projector applications requiring a high luminance concentrated as far as possible at a spatial point. In the projector applications, a concentrated heat sink can be actively cooled without any problems, e.g. by means of a fan airstream. Ballasts used are usually special complex switch mode power supplies which are adapted to a low voltage of the LEDs and are additionally embodied in a manner potential-isolated from an electricity grid, such that an electrode of the LEDs can be designed as a heat dissipater.
The light color of an LED lamp including different-colored LEDs has previously been set by altering an electric current through the different-colored LEDs. This means that the individual different-colored LEDs or LED groups are each equipped with a dedicated controllable current driver. The light from the LEDs is mixed by means of a diffusely reflecting screen such that the luminous device exhibits as far as possible a color or color effect that is uniform in all emission directions and over the entire light emission area.
However, color regulation is often dispensed with if blue LEDs are used which are surrounded directly by a wavelength-converting phosphor that converts part of the blue light into a differently colored, e.g. red-yellow-green, radiation (“color conversion LEDs”), such that a white mixed light arises overall. The color impression is thus substantially fixed, however, apart from variations governed by an operating current, a temperature and also an aging degradation of LED(s) and colorant. This means that the (mixed) color of conversion LED luminous devices has to be set from the start by means of a very precise selection of the LEDs or LED chips. This in turn imposes stringent demands on a color measurement technology of the LED (chips) and manufacturing control. Compensation of the variation of the color or color impression on account of a change in temperature and/or an age degradation is not possible or is possible only to a very limited extent by means of a change in the operating current (which in turn changes the light intensity, however). Moreover, ascertaining a color change and correcting it have previously required a cost-intensive sensor and electronics connected downstream.